This invention relates generally to a composition and a method for suppressing bark beetle development and, more particularly, to a composition and method for preventing and controlling infestation of pine trees by southern pine beetles and associated bark beetles.
Bark beetles and particularly southern pine beetles (Dendroctonus frontalis Zimmerman) are endemic to many forests. When temperature, rainfall and other conditions are right, they may multiply on a prodigious scale, producing swarms of one million or more beetles per acre. As many as 100,000 to 150,000 southern pine beetles may attack successive pine trees, killing them on an epidemic scale. Although it takes 35 years to grow pine trees that are harvestable for lumber, pine bark beetles can cause devastation of pine forests in a few weeks.
Female beetles initiate the attack on each tree, producing pheromones to attract male beetles. The females bore into the tree and the pheromones guide the males to them. After each pair of beetles mates, they dig a gallery on the underside of the bark into which the female deposits up to 30 eggs. The eggs hatch into larvae roughly seven days after they are laid and the larvae feed for about two weeks producing larvae mines. The larvae then pupate in the bark for seven days and finally adults emerge from the pupa chamber by boring a small hole out through the bark. The galleries and larvae mines disrupt the cambium layer of the tree, weakening its life-support system and, by mechanisms which are not well understood, eventually kill the tree. The lumber grade and yield from beetle-killed trees are significantly reduced, particularly where harvest is delayed. In addition, the beetles carry a fungus which stains the pine wood blue, further reducing its commercial value.
Although pine trees have natural defense systems which usually limit beetle damage, when the numbers of beetles are overwhelming, the defense systems fail. It is generally agreed that the primary defense of southern pines is the preformed oleoresin system. Attacking beetles sever resin ducts, releasing their contents. The action of released compounds may be: (1) direct toxicity, (2) flow, viscosity, and crystallization characteristics that result in beetle "pitch-out", or (3) prevention of the introduction of beetle associated microorganisms that could alter tree physiology and lead to its death.
Man similarly has no effective method for handling pine beetle infestations. The application of conventional insecticides, for example, has been ineffective because it is extremely difficult to locate infested trees until the destruction has reached an advanced stage. Also, many insecticides indiscrimately harm bark beetle predators and parasites which otherwise help to naturally control the beetles.
The most common approach to controlling southern pine beetle and other bark beetle infestations has been to fell infested trees and either leave them in the forest or haul them out for salvage. This is an expensive, labor-intensive technique. Furthermore, when the diseased trees are sold for salvage, distress prices are typically the best that are available, due both to the damage to the timber and to the large quantity of such timber coming to market. In one popular alternative approach called "cut-and-leave", currently infested but still active trees and a buffer strip of uninfested trees are cut so that they fall towards the center of a grouping or "spot" of dead trees. This technique, which is intended to stop the expansion of the spot, unfortunately, is only of very limited effectiveness in controlling the spread of the beetles.